There is substantial literature in the art with respect to the hydrogenation of methylene bridged polyphenylamines to produce polycyclohexylamine counterparts using a hydrogenation catalyst. A material for which there has been substantial hydrogenation activity effort is methylenedianiline with the end product being bis(4-aminocyclohexyl)methane; it is also called bis(para-aminocyclohexyl)methane or PACM. Some of the early work was done by Whitman and Barkdoll, et al. and their work is set forth in a series of U.S. Pat. Nos. e.g., 2,511,028; 2,606,924; 2,606,925; and 2,606,928. Basically the processes described in these patents involve the hydrogenation of methylenedianiline at pressures in excess of 200 psig, preferably in excess of 1,000 psig, at temperatures within a range of 80.degree. to 275.degree. C. utilizing a ruthenium catalyst for the hydrogenation. The hydrogenation is carried out under liquid phase conditions. Usually an inert organic solvent is used in the hydrogenation process. Examples of ruthenium catalysts utilized for the hydrogenation process include ruthenium oxides such as ruthenium sesquioxide and ruthenium dioxide; and ruthenium salts.
Brake, et al. continued with the development of hydrogenation process to produce PACM and they found that if the ruthenium catalyst was carried upon a support and the support alkali-moderated, the catalyst was much more active and catalytically effective in producing the desired hydrogenated PACM product. Alkali moderation was effected by contacting the catalyst and support with alkali metal hydroxide or an alkoxide; also, such alkali moderation of the catalyst could be effected prior to hydrogenation or in situ during the hydrogenation. Representative patents showing the utilization of alkali moderated ruthenium catalysts to hydrogenate methylenedianiline include U.S. Pat. Nos. 3,636,108; 3,644,522; and U.S. Pat. No. 3,697,449. Alkali metal and alkaline earth metal nitrates and sulfates have similarly been shown effective in U.S. Pat. No. 4,448,995 under high pressure (4000 psi) hydrogenation conditions.
Other catalysts have been utilized for the hydrogenation of methylenedianiline and examples are shown in U.S. Pat. No. 3,591,635 and U.S. Pat. No. 3,856,862. Both patents disclose the use of rhodium as a catalytic material and each require the use of an aliphatic alcohol as a solvent. The rhodium is alkali moderated using ammonium hydroxide as a pretreatment or by carrying out the reaction in the presence of ammonia. Also, in European application 66,212 rhodium on alumina in the presence of butyl ether is disclosed to obtain 15-50% trans, trans-isomer ratio contents, but again the pressures are high (4000 psi) and the reaction times short, leading to difficult reaction product control.
In the catalytic processes for hydrogenating methylene bridged polyphenylamines as described above, the bridged polyphenylamines were purified, i.e., distilled to remove trace impurities and oligomers. Crude polyphenylamines were difficult to hydrogenate presumably because impurities in the feedstock poisoned the catalyst. U.S. Pat. No. 3,959,374 describes a process for the catalytic hydrogenation of methylene bridged polyphenylamine which contained trace impurities and oligomers. More specifically a crude methylenedianiline feed containing these impurities and oligomers is initially treated with hydrogen in the presence of a nickel containing hydrogenation catalyst prior to hydrogenation in the presence of a ruthenium catalyst. The pretreatment overcomes low yields (52.4%) and long reaction times associated with nickel and cobalt. In the absence of the pretreatment, ruthenium catalysts, although commonly used for hydrogenation of purified methylenedianiline, were not suited for hydrogenation of a methylene dianiline feed containing impurities, e.g., isomeric impurities.